Backdoors in your smartphones? Why? How ? Not?

As smartphones become increasingly secure and end-to-end encryption is now widely used, governments and law enforcement face growing challenges in accessing digital evidence. In response, new technical and legal mechanisms have been proposed, such as client-side scanning and lawful access frameworks. On the legal side, European initiatives such as ChatControl are pushing for massive scanning of exchanged content using perceptual hashing. On the French side, the narcotraffic law attempted to mandate backdoors in chat applications, while an article in the (still under discussion) resilience law tries to make backdoors illegal. But can secure systems remain secure while still guaranteeing exceptional access? This talk examines what "backdoors" really mean from a systems and protocols perspective, and discusses concrete technical proposals. It highlights scientific results and real-world examples that expose fundamental limitations and unintended consequences of some of these approaches.